Did you arrive at that conclusion driven by observation and evidence? If so, then that means you notice this behaviour only on the politics threads. Now, ask yourself: are people here really not behaving analytically and logically only when it comes to politics, but you only happen to notice that when it comes to politics? Or maybe you only think that this happens in politics because you have an unreasonably emotional reaction to truly analytical points of view that contradict your political view points?
This wouldn't rule out the above, both reasons can coexist even, but it'd add to the understanding significantly.
You second sentence does not follow from first one. It is quite possible for HN to have that behavior in more then one topic while OP making the first observation in politics.
That’s why people who might otherwise have a logical and analytical approach to technical matters forget how to apply that when it comes to these topics.
That is also the reason why politics and religion are not generally “allowed topics” on this forum except when directly related to tech or a major world event.
I think generally speaking political discussions are discouraged on HN for this precise reason.
Personally, I find the HN crowd to be very logical and intelligent on most issues, though there are some pockets of ignorance and SJWs. However, much of that ignorance is fueled by external motivations and misguided desires.